Integrins are a superfamily of cell surface receptors that mediate cell-cell and cell-matrix adhesion. These proteins are known to provide anchorage as well as signals for cellular growth, migration and differentiation during development and tissue repair. Integrins have also been implicated in cell dedifferentiation and invasion, notably where cells lose their specialized form and become metastasizing cancer cells.
Integrins are heterodimeric proteins composed of two noncovalently linked subunits, α and β. The binding specificity of integrins is dictated by the combination of some 18 different α chains with some 8 different β chains. The αvβ6 integrin can bind to a number of ligands including fibronectin, tenascin, vitronectin, and the recently identified latency associated peptide “LAP,” a 278 amino acid peptide synthesized as part of the precursor TGF-β protein (Munger et al., Cell 96(3):319-328 (1999)). LAP is cleaved from the mature form of TGF-β as an N-terminal peptide during secretion but remains noncovalently associated with TGF-β to maintain its latent state. This complex cannot bind to the TGF-β receptor and hence is not biologically active. The αvβ6 integrin can bind directly to an RGD motif contained within LAP, resulting in release of LAP and activation of TGF-β. Since αvβ6's binding to LAP may be important in the conversion of TGF-β to its active state, blocking the binding may result in inhibition of αvβ6-mediated activation of TGF-β and the associated fibrotic pathology.